Signal detectors and methods thereof are known. Signal detectors have been arranged to detect signals in the presence of an interfering signal with varying degrees of success. In most cases there is a fundamental tradeoff for these detectors between false positive and false negative errors. False positive errors is where the signal detector indicates the signal has been detected when no such signal was present and false negative errors is where the signal is actually present but is not detected. In many detectors the incidence of false negative errors can be improved but at the expense of false positive errors and vice-a-versa.
One particular example of a signal within an interfering signal is a Customer premises equipment (CPE) Alerting Signal (CAS) or CAS tone used by telephony local service providers for local loop signaling where customers have Caller ID on Call Waiting (CIDCW) service. The CAS tone is an 80 millisecond duration, in band, dual tone (2130 Hz, 2759 Hz), −22 dBm signal that is sent from a central office switch (CO) to a CPE that can detect the CAS tone in the presence of the interfering signal, namely speech, music, and the like. Generally when a customer is on the phone or off hook and a call for the subscriber comes in the CO mutes the line and sends a subscriber access signal (SAS) followed by the CAS signal. The CPE detects the CAS, mutes the local person and sends an acknowledge tone, specifically DTMF D. The CO detects this acknowledge tone and sends the Caller ID information for the waiting call. Thus if the CAS detector has a false positive error or false detection, often referred to as a talk off the users voice will be muted for approximately 500 milliseconds and conversely a false negative error or failure to detect the CAS tone, typically referred to as a talk down error the customer will not receive the expected caller ID information for the waiting call.
To encourage widespread adoption of CIDCW a rigorous standard for the performance of CAS detectors has been developed by Bellcore. Generally this standard requires a detection rate of 99.5% and limits false detections to <1 per 45 hours. Clearly a need exists for a high performance low complexity signal detectors and methods therein.